Subject: RE:[Sip] Distinguishing subscription from polling resource state

From: [email-masked]
Date: Wed, 23 Nov 2005 12:04:51 +0530

Hi Tim,
 yes,you can consider these conditions to distinguish between poll and
 terminate subscription

 Regards
 Nagendra
 FSS, Bangalore.

 To: <[email-masked]>
 From: "Tim Rang" <[email-masked]>
 Sent by: [email-masked]
 Date: 11/23/2005 06:32AM
 Subject: [Sip] Distinguishing subscription from polling resource state

 I have an issue regarding RFC 3265 section 3.3.6 ? Polling Resource State
 ?.  It is clear that a SUBSCRIBE request with an Expires value of 0 may
 constitute a resource query or an unsubscribe, depending upon whether a
 dialog exists.  If I have a proxy server wants to distinguish between
 unsubscribe and resource query, and my proxy server does not maintain
 dialog state, what message element(s) can it use to make that
 determination?

 My position is that you can use the To tag parameter (or lack of).  On
 reading through 3261, 12.1.2 states that To tags should not be expected as
 they were not mandated in 2543 (there seems to be a lot of this lately).
 However, 2543 states in section 6.37-

   ?It MUST be placed in the To field of the response by each instance when
 there is a possibility that the request was forked at an intermediate
 proxy.?

 That RFC is silent on when it is ok to omit.  My read of this is that a
 UAS can only ?know? that a forking server was NOT in the path in one
 condition- if the request was sent peer to peer, without any proxy servers
 in the path.

 Accepting that, and knowing that my question is unique to scenarios when
 proxies are involved, is it ok to assume that any SUBSCRIBE request sent
 by a UA (either 3261 or 2543 compliant) which passes through a proxy meets
 the following conditions-

          - if a tag parameter is present in the To header, then the
          SUBSCRIBE (Expires=0) is in fact an unsubscribe.

          -
                                                                            
          If a tag parameter is NOT present, the SUBSCRIBE (Expires=0) is a 
          polling subscribe?                                                

 Thanks,                                                                    

 Tim Rang                                                                   

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